Prosthodontics is the specialized branch of dentistry which deals with repair or replacement of damaged or missing teeth which are lost due to poor dental hygiene, disease or injury. Replacement of missing teeth is important to provide proper mastication and speech, to avoid overstressing or unwanted movement of remaining natural teeth, and to maintain good facial appearance.
A fundamental problem in restorative dentistry is the method of attachment or anchorage of the artificial tooth or teeth. Historically, fixed or removable appliances supporting the artificial tooth or teeth have relied on attachment to adjacent natural teeth, and this anchorage method typically involves some unwanted removal of structure of the adjacent natural teeth to provide attachment sites. In the more difficult case of a patient with no remaining natural teeth in one or both of the upper and lower dental arches, complete dentures are constructed to fit over the ridge of gum tissue which overlies the supporting upper or lower jawbone. Anchorage of a complete denture is imperfect, and frequently a source of discomfort and annoyance to the patient.
In recent years, dental implant bodies have been developed to provide a greatly improved solution to the problem of anchoring a single artificial tooth or an appliance supporting two or more artificial teeth. An implant body is typically a metal body of cylindrical shape which is threaded or otherwise fitted into a mating hole drilled in the jawbone in a surgical installation procedure.
Implant bodies are usually made of titanium which is both strong and biocompatible with the bone. Apertures or irregular surfaces may be provided on the implant-body exterior, or alternatively the exterior may be coated with hydroxyapatite to encourage bone growth around and into the implant body for increased anchorage during the healing process which may take from two or three up to six months. After surgical implantation and during the healing process, the overlying gum tissue may be closed over the gingival facing end of the implant body.
When the healing period is over, and the implant body is firmly secured in the jawbone by a process called osseointegration, the gum tissue is incised to expose the gingival end of the implant body which is provided with a threaded socket (or alternatively, a threaded post) or similar attachment site. A transmucosal healing cap is installed in the incision and screwed into the implant body. The patient is then referred to the restoring dentist, and a superstructure called an impression post is secured to the attachment site to extend transmucosally through the gum tissue into the space where an artificial tooth or multiple-tooth appliance is to be mounted.
A conventional impression is then taken of the dental arch, with the impression post in place to form a socket in the impression material. When the hardened impression material is removed from the mouth, the post is removed from the implant body, and placed in the impression socket. An implant analog (a metal body generally corresponding in shape to the now-embedded implant body in the patient's jawbone) is threaded on the post end which extends from the impression, and a conventional stone (dental plaster) model is then poured in the impression. The stone model reproduces the contours of the patient's teeth and gums, and the implant analog is positioned within the stone model in the exact position of the implant body embedded in the jawbone.
A dental-laboratory technician then removes the impression post, and attaches a tapered biocompatible post called an abutment to the implant analog. The abutment will later be attached to the implant body in the patient's jawbone to provide a solid attachment site for a prosthesis.
The technician then uses the stone model to construct an artificial tooth or multi-tooth prosthesis for eventual installation over the abutment or abutments in the patient's mouth. Bone anchorage of the implant body provides a solid attachment for the abutment, and hence secure anchorage for the installed prosthesis which may be cemented to the abutment or abutments, or otherwise secured if the prosthetic appliance is of the removable type.
Implant bodies have enjoyed significant success in restorative dentistry, but the inability of an oral surgeon to achieve routine ideal placement and alignment of the implant body in the jawbone creates a problem. Such ideal placement would position the longitudinal axis of the implant body, and hence the axis of the abutment, in a centralized location enabling the prosthesis to be placed in the desired position. The problem is aggravated where multiple implant bodies are installed to provide multipoint anchorage for a bridge or complete denture, and the abutment axes must be substantially parallel to enable prosthesis insertion. The problem of implant-body misalignment is typically present in a patient with eroded, weak or degenerated bone structure of a cross section which requires implant body insertion in a non-ideal orientation. These difficulties are discussed in greater detail in U.S. Pat. Nos. 5,052,929, 5,195,891, and 5,209,666, and, for brevity, the disclosures of these patents are incorporated herein by reference.
The present invention provides a solution to the problem of implant bodies which are necessarily placed in the jawbone in a non-ideal axial orientation. The invention enables a dental-laboratory technician to create a custom-shaped cast abutment which is angulated to correct the misalignment of the associated implant body, and which incorporates a precision metal base which mates perfectly with the implant body.